Revascularization of obstructed coronary arteries by percutaneous transluminal coronary angioplasty (PTCA) has become an integral component of front-line treatment programs for patients with ischemic heart disease (Vaitkus, P. T. 1995, Coron. Atery Dis., 6:429-439). Although acute complications of PTCA have markedly declined with optimized use of anticoagulants, antispasmodic agents, and intravascular stents, the incidence of coronary artery restenosis has remained at 30%-50% and represents the major obstacle to a more successful outcome of PTCA (Landzberg, et. al., 1997, Prog. Cardiovascular Diseases, 39:361-298). Therefore, the development of effective strategies for restenosis prophylaxis has become a focal point for translational cardiovascular research.
The pathogenesis of restenosis has been compared to an exaggerated wound healing response with migration of smooth muscle cells from the media to the intima of the revascularized coronary artery where they proliferate and cause an obstructive neointimal hyperplasia (Ueda et al., 1995, Coron. Artery Dis., 6:71-8 1). Many factors contribute to the development of restenosis, including vascular injury, platelet aggregation, procedural factors, inflammation, and mitogenic stimulation of migration and proliferation of smooth muscle cells. The relative contribution of any one of these factors remains unclear.
Pharmacological approaches to prevent restenosis include antiplatelet and antithrombotic agents, anti-inflammatory drugs, growth factor antagonists, vasodilators, antiproliferatives, antineoplastics, photochemotherapy, and lipid lowering agents. Some growth factor antagonists have also been studied for effects on restenosis.
Inhibition of vascular smooth muscle cell proliferation by a platelet derived growth factor (PDGF)-antagonist has generated promising results in preclinical as well as early clinical studies, thereby confirming the biologic importance of vascular smooth muscle cells in the pathophysiology of restenosis (Mullins et al., 1994, Arterioscler. Thromb., 14:1047-1055).
Targeting Genistein (Gen) (5,7,4'-trihydroxyisoflavone), a naturally occurring tyrosine kinase inhibitor present in soybeans (Aikyama ET.AL., 1987, J. Biol. Chem, 262:5592-5595; Uckun et al., 1995, Science 267:886-891) to the EGF-receptor/PTK complexes in breast cancer cells using the EGF-Gen conjugate resulted in marked inhibition of the EGF-receptor tyrosine kinase and EGF-receptor-associated Src family PTK (Uckun et al., 1998, Clinical Cancer Research, 4: 901-912).
Proliferating vascular smooth muscle cells also express high levels of the EGF-receptor (Saltis et.al., 1995, Atherosclerosis, 118:77-87). Furthermore, as described more fully in the Examples below, a noninvasive small animal model of restenosis (FIG. 1), which employs photoactivated rose bengal to induce vascular injury to the femoral arteries of C57B 1/6 mice leading to neointimal hyperplasia mimicking the post-PTCA restenosis of coronary arteries, demonstrated that the myofibroblasts of the neointima were EGF-receptor positive in 8 of 8 mice (100%) analyzed. Notably, the neointima of the injured femoral arteries stained more intensely with the anti-EGF receptor antibody than the media and/or intima of uninjured femoral arteries.
These findings suggested that the EGF-receptor function and EGF-receptor-linked signal transduction events may be essential for the migration and proliferation of myofibroblasts contributing to the neointimal hyperplasia after vascular injury. It was then postulated that the EGF-receptor on vascular smooth muscle cells may be a suitable target for restenosis prophylaxis using EGF-receptor-directed tyrosine kinase inhibitors such as EGF-Genistein.
Development of prevention and treatment methods for vascular restenosis remains an important goal of cardiovascular research. Currently there are very limited treatment options available to prevent or treat restenosis, particularly following PTCA. Accordingly, there is a need for specific and effective therapeutic treatments for the inhibition of restenosis, particularly for patients undergoing coronary angioplasty.
Several animal models have been developed for studying restenosis. Major blood vessels of rats, rabbits and pigs have been subjected to injury from balloon or stent mediated treatment. Porcine coronary arteries seem to be the most predictive of the human response. However, many of these models are not amenable to large scale screening of prophylactic or therapeutic agents. Accordingly, an animal model of restenosis that can be used for large scale screening of therapeutic and prophylatic agents is needed.